Yet another gardening post. If you have no interest in growing cucurbits, stop now.
This is summary of everything I think I have learned about the squash vine borer (SVB). All in one place. Off the top of my head, based on what I’ve read over the past week, and what I’ve observed in my garden. So I can remember it next year. Citations as to source only if and as I feel like locating them.
This isn’t finished yet. But I thought there was enough useful information that I would go ahead and put it up now. Because, having read the literature, I’ve decided on what I’m going to do to try to control the SVB. I explain what I’m doing, and why, in the Executive Summary below. Click this link to go directly to that section.
In case you don’t know what this is, the SVB lays eggs that hatch into larvae that eat their way into the stems of your cucurbits, and kill them. So if you grow summer squash, winter squash, pumpkins, and to a lesser degree cucumbers or melons, just a handful of these can destroy your crop.
I’ve never run across them before, in 25+ years of off-and-on gardening in Vienna, VA. But I surely have them this year. First noticed one on 7/5/2020; saw one in the garden yesterday 7/13/2020. They only live about five days, so at this point I presume that I’ve had a succession of them, even though I only see one at a time.
Arguably, I have attracted them this year because I made myself a target. I ended up planting a large garden that’s mostly cucurbits.* Not intentionally, just because other crops failed.
* Including 16 summer squash, 12 winter squash, 6 pie pumpkins, maybe 12 field pumpkins, and a couple of dozen cucumbers. In short, an SVB smorgasbord.
An excellent and compact scholarly reference can be found at this URL: University of Florida. That said, there is disagreement across sources on some key details.
When does the SVB moth appear? These pests show up between 750 and 1000 growing-degree-days (GDD) into the summer. (GDD, and sources showing local GDD, are given in the body of the posting). If the 1000-GDD figure is right, then these would show up just after the Japanese beetles. So that may (or may not) give you a reliable clue as to when to start looking for them.
How long are they around laying eggs? It’s not clear how long the moths stay around laying eggs in this area. Much internet chatter suggests that it’s just a week or two. But that may or may not apply to Virginia, and I have yet to find a reliable source telling me what the typical season length is in Virginia. For sure, some locations (New Hampshire, cited below) show a month-long season or more for SVB moths, with the possibility that a second generation of SVB moths can emerge during a warm summer (in norther states), or the certainty of a second generation (in Florida and the rest of the Deep South). In short, you may have these things laying eggs on your squash plants for weeks and weeks.
What plants are at risk? The SVB will lay eggs on almost anything in the cucurbit family. But everyone agrees that summer squash are the prime target, with zucchini being more at risk than yellow squash. After that, some pumpkins are targets. Larger-stemmed and hollow-stemmed cucurbits are preferred to smaller-stemmed and solid-stemmed cucurbits. Apparently small-stemmed winter squash such as butternut are poor targets, and tolerate SVB well. In theory, cucumbers and melons are rarely affected, but there are plenty of case reports of gardeners losing entire cucumber crops to SVB.
When will damage appear? It takes the eggs 7 (possibly 9) to 14 days to hatch. Then the borer has to grow to a size that affects the plant. So, best guess, something like three weeks after the first SVB moth appears.
How can you protect your plants: Prevention. I’m still working on this one, trying to sort out which of the proposed methods actually works. Plus, I started late in the game here, after the SVB arrived.
One commonly-suggested method is to wrap the squash stem in tin foil or pantyhose. That would work for vining squash, but I don’t think that would work for summer squash. For sure, based on reliable sources and my own observation, if you rely on wrapping the stem, you need to wrap a foot or two of stem, not just the bottom inch or two. I’ve definitely observed the SVB ovipositing on parts of the stem that were a foot off the ground.
Some sources suggest trying to trap the moth with yellow bowls filled with soapy water, as they are attracted to the yellow of squash blossoms. This is a non-selective method and apparently results in killing anything else attracted to squash blossoms (e.g., bees). I have not tried this. I have also seen references to coating the lower stems with Tanglefoot. That seems reasonable to me, as bees would have no reason to light on the lower stems, but I have not tried this nor have I seen any estimates of effectiveness at trapping the SVB moth.
Many sources suggest planting a trap crop of (e.g.) Blue Hubbard squash, which is very attractive to SVB. I assume that most gardeners in this area do not have the space to devote to a trap crop. From what I can see in my garden, the SVB lays eggs on every cucurbit regardless. They started with the summer squash, but I’ve seen them on every cucurbit I have, other than cucumbers. One source suggests interplanting with cucumbers as a way to discourage SVB.
How can you protect your plants: Killing the larvae before they enter the vines. I’m limiting discussion to “organic” pesticides. Also, per the “weeks and weeks” above, you need to plan for multiple rounds of spraying, because the SVB moths may be depositing eggs for a month or more. All the more reason to avoid (e.g.) persistent synthetic poisons.
Of the “organic” poisons: Pyrethrins seems to have the highest potential for bee toxicity, so I ignored that. BT is bee-safe and will, in theory, work on SVB larvae in the brief interval between hatching and burrowing into the stem. But BT is quite short-lived and so would require frequent (every-other-day?) spraying of the stems of the plants. Spinosad is thought to be bee-safe when dry, if not sprayedwasp directly on blossoms. It is supposed to be as effective as pyrethrins in this use, so I am using that. There are also internet reports of good effects with neem oil (also presumed bee-safe if used reasonably), though what, exactly, that is doing is not clear (smothering eggs, disrupting egg life cycle, disrupting larval life cycle?). The best case report I read suggested that using neem as a systemic poison — dosing the plants on a regular basis, as they grow, well before before the SVB arrives — seems to work particularly well. That suggests to me that a primary mechanism of action may be literally poisoning whatever larvae actually make it into the stems of the plants.
Diatomaceous earth is mentioned in many references, but a) I could not find out whether there has been any test of effectiveness, and b) it washes off with each rainstorm. I don’t even know if the diatomaceous earth was intended to target the larvae (in the brief interval between hatching and entering the plant stem) or the SVB moth itself.
What am I doing? I am spraying spinosad weekly, in the evening (after the bees are gone), spraying the first couple of feet of every stem of every cucurbit in my garden. I am not using pre-mixed spray (Captain Jacks Deadbug Juice)s, but instead am using concentrate that, when mixed per directions, results in about 8 times higher spinosad concentration than the ready-mix. I’m going to continue to do this for two weeks after I see the last moth. As far as I can tell, based on the vibrant bee population in my garden, this has not hurt the bees at all. I also kill every one of these SVBs that I can manage to catch, but they are hard to kill by hand.
Edit: No, see next post. I’ll spray it, maybe, but I’m not going to do a “soil drench” because there are too many unknowns. I also like the idea of injecting neem into infested stems, as others have reported doing with BT, to kill the larvae in situ without slicing open the stems.
I am also getting ready to soak the soil around the squash stems with neem on a regular basis, starting this PM . Plants readily absorb the active ingredient of neem via their roots (and only weakly though the leaves). I am hoping to achieve systemic poisoning of any SVB larvae that make it into the stems, via neem. I am only doing this for the most vulnerable species (summer squash and pumpkins). For this, there should be little to no potential for bee toxicity.
In short, I am protecting the exterior of the stem with spinosad, which should, in theory, poison the larvae as they chew through the stem. And I plan to protect the interior of the stem by
introducing neem at the roots and hoping to achieve systemic insecticidal activity.
How can you protect your plants: Killing the larvae after they enter the vines. I haven’t gotten to that point yet, but in theory, you can slice open the vine, extract the larvum, and re-bury the vine. Some people also suggest injecting BT into the vine, but I do not know the effectiveness of that. Others suggest other physical methods (e.g., sticking pins into the vine repeatedly to kill the borer larvae). Effectiveness unknown. EDIT: Also, see next post, there is at least one case report of using neem oil as described above for BT (inject it into the vine at the site of borer infestation.)
Instead, as noted above, I’m going to attempt to get systemic insecticide protection by having the plants take up neem via their root systems. This is the same concept as BT injection, but more automatic — poison the larvae within the plant stem itself.
There is some agreement that vining squash that are allowed to root at each vine node are more robust to SVB attack, because they are not dependent on a single set of roots to survive. This has implications for trellising squash to save space, as trellised vining squash depend on a single set of roots.
What do I wish I had done, and may yet do? Anything that would kill or deter the SVB moth. This includes: Sticky traps at the bases of the plants. Possibly, diatomaceous earth on or around the same locations. Near as I can tell, both of these approaches target the moths, not the larvae. Possibly, wrapping the first foot or two of stems of vining cururbits (not feasible for summer squash).
First things first: Kill them when you see them.
I killed my third squash vine borer (SVB) moth two days ago. It’s not so easy to do by hand. The damned things are fast and skittish. They land on squash leaves, which are fragile. After fumbling my first few attempts, I have developed the following technique.
They will often sun themselves in mid-afternoon on the leaves of your squash. I find that 3:30 PM is a good time for hunting. Don’t try to brush them to the ground and stomp them. Don’t try to pick them off. They’re too fast. At least, they were too fast for me. Fast enough that you’ll lose track of their flight almost instantly, despite the fact that they are brightly colored. Slowly place one hand under the leaf, then clap your hands together to kill the moth. Wear a glove if you’re squeamish. I’m batting a thousand with that method.
I also note that they’re easy to spot when they fly, due to their bright color. Keep a lookout when you’re in the garden. In flight, they are almost unmistakable.
I’ve had a hard enough time killing them by hand that I’m considering buying a bug vaccuum, or even getting a can of something really toxic to spray them with.
Timing: when do they show up, how long do they stay.
Lots of detail follows, but here are the key basics:
- The adult moths (probably, typically) emerge just after the Japanese beetles. That’s handy, because the far-more-numerous Japanese beetles are a lot easier to spot. Japanese beetles take about 970 growing degree days of warmth (see below) before they emerge. The SVB takes about 1000. (But other scholarly sources put the SVB emergence at 750 to 1000 growing degree days, which would mean that they could show up well before Japanese beetles. And, in fact, we passed 1000 growing degree days some weeks ago. So I’m not sure how accurate any of that information is.) In any case, timing relative to Japanese beetles matches my observation here in Vienna, this year. I had just put up a couple of Japanese beetle traps when the SVB showed up. (By the way, I have round those new lure-based Japanese beetle traps to be incredibly effective.)
- The females lay eggs that take 8 to 14 days to hatch (per scholarly reference above). (Other references put it at 9 – 14, and note that it depends on temerature — warmer = faster.) Therefore, if you plan to eradicate the larvae before they get into your plants, you want to keep some sort of caterpillar-killing poison on your cucurbit stems from the first day you see one + 8 (earliest possible larval emergence) to the last day you seem one + 14 (latest possible).
- For me, as of today (saw yet another yesterday 7/13/2020), that means from 7/13/2020 through at least 7/27/2020. Assuming that I noticed them on the first day they were here. And assuming that I don’t see another one tomorrow. In short, you need to plan for a weeks-long campaign in order to try to save your crop, once these show up. Assuming you stay away from persistent pesticides. A single spraying of any non-persistent pesticide isn’t going to hack it.
- And the really bad news is that in some locations, SVB moths can keep showing up for more than a month. And if the weather is warm, around here you may have two generations appear in a single season. That means you’ll have to plan on at least a six-week campaign of spraying if you want to keep your squash crop. Here’s a count of months trapped in one New Hampshire location.
On that last point, this directly contradicts common social-media information that says that once you’ve seen the squash borer arrive, it’s safe to plant a second crop. That may be true in some areas, but clearly is not true in other areas. In the Deep South (e.g.) Florida, they routinely have a second emergence of these during a single summer. But while a second generation is typical in warmer climates, it is not in colder climates. We’re in the middle. I have not yet found information on the typical SVB season length in this area.
The practical upshot is that, based on social-media information that probably doesn’t apply in this growing area, I haven’t taken any preventative measures (e.g., sticky traps). A) I figured it was too late, and B) I figured they’d be gone in a week. Both those assumptions may have been wrong. I may have female moths laying eggs for weeks yet. That will depend on how long the squash borer months stay around, and whether or not we have a second generation emerge. I should probably have started preventive measures (e.g., sticky traps) as soon as I saw my first moth.
That said, the University of Maryland extension service seems to indicate that you can dodge these pests around here by timing your planting accordingly. That implies a single short season for SVB in this area. They say: “Plant early to lessen injury. Use transplants instead of seeds. Or, plant squash seed mid-June.” But it’s not clear whether they are just quoting conventional wisdom, or whether they have actually measured the length of the season for SVB locally.
The upshot is that you have to keep being on the lookout for these pests, once they arrive.
A ludicrous amount of detail follows.
The SVB over-winters in cocoons in the soil, and emerges somewhere around 950 to 1000 Growing Degree Days (GDD, explained below) into the summer. I noticed my first one on 7/5/2020, here in Vienna, VA. No telling how long they were around before I spotted one. But I was casually keeping an eye out for them because the majority of my garden this year is cucurbits.
I noticed the SVB maybe a week after I started noticing significant numbers of Japanese beetles around the garden. That’s not a coincidence, as the Japanese Beetle emerges somewhere around 970 growing degree-days, per this reference. And, in fact, I had hung up a Japanese Beetle trap maybe two days before I saw my first SVB. I’d say the Japanese beetles arrived maybe a week before I spotted my first SVB. So, around here at least, I think the emergence of the easily-spotted Japanese beetle tells you to be on the lookout for the SVB.
In fact, that “natural” method may be more accurate that the strict calculation of growing degree days.
Degree-day drill down: First, that’s NOT your heating-cooling degree days. This is your “growing” degree days using 50F as the base temperature. That 50-degree reference point is more-or-less a standard in agriculture, and appears to be the cumulative time during which the temperature exceeds 50F. In Virginia, Virginia Tech would be the place to get information. A nice general reference is available from the American Public Gardens Association.
Note that GDD comes in at least two different varieties, with Corn GDD capping the temperature at 86F, because corn stops growing appreciably when it gets that hot. I presume that for insect pests, I want to see GDD, and not corn GDD. You can also see it calculated with bases other than 50F. Finally, the true-and-accurate calculation requires hourly temperature data, but as far as I can tell, virtually everything you can find on line uses an approximation based on the mean of the minimum and maximum temperature for the day.
According to this site, we passed 1000 GDD back on June 22. That’s almost two weeks before I spotted my first SVB. However, I can infer from the values that they are using a simple approximation (average of max and min temperature, less 50, as described by NOAA) in their calculation. Yet, this site, from Cornell University puts the 1000-GDD threshold at June 24 for Vienna this year.
That’s well before I spotted any significant number of Japanese beetles. I’m taking all of this as an indication that you can’t really do (or get) a precise growing degree day calculation that will tell you, with certainty, when to expect the SVB.
Plus, the things are good fliers. Apparently, can fly up to a mile from where they hatch, to your garden. So they may arrive some significant time after they hatch. Near as I can tell, using the presence of Japanese beetles as a warning flag is probably more reliable than doing the growing degree day calculation.
Risk: Which cucurbits?
Here, I am supposed to offer some sort of reassuring list. Oh, they like zucchini, but your butternut squash should be OK. And your cukes are probably not at risk. As if some cucurbits were at risk, and others were not.
Surely you can read up on what’s most and least at risk, and do not have to have that repeated here. Big, hollow-stemmed summer squash are at the top of the list (zucchini first, then yellow summer squash), followed by other large-stemmed cucurbits (pumpkins), then winter squash (I guess), then cucumbers and melons.
Here’s my observation. That’s really a list of what they’ll hit first, versus what they’ll hit later. But if you have enough of them, they’ll hit every cucurbit in your garden, at least as far down the list as cucumber.
Based on my observation, I believe there’s an order of preference that corresponds to the lists you’ll find in various references. I.e., nothing is safe, it’s just a question of what’s more at risk.
So, in my case, sure enough, the first thing I saw them ovipositing on was, in fact, zucchini. Later I caught one napping on some pumpkin leaves. I’ve seen them buzzing my butternut (winter) squash. The only thing I haven’t directly seen SVB on is cucumbers (and I have a lot of cucumbers planted).
I strongly suspect that the moths can tell if another moth has laid eggs on a plant. And so, as a species, they’ll just run through your garden, from most to least desirable target. Each moth only lays maybe 200 eggs max. So it’s first come, first served, on your cucurbits. First moth hits the best target, which is zucchini. I haven’t seen them on the zucchini since the first day. The latecomers then hit what’s left. To the point where this morning’s moth was on the sole outlier (a pumpkin that I planted, on a whim, in my sunflower patch).
Plants also vary in the susceptibility. As I understand it, unchecked, the SVB will kill summer squash outright, and in a short time period. The SVB will typically just damage others and reduce their yield.
I think that’s in large part due to secondary root systems on vining curcubits. Summer squash are both desirable to the pest, and vulnerable because they have a single short stem and a single root system. By contrast, vining squash put down secondary roots (where possible) at each node on the vine. These secondary root systems prevent the borer from killing ground-grown vining curcubits outright. But note that If you are growing (e.g.) winter squash on trellises, you don’t get that protection from secondary roots farther down the vine.
But my bottom line is that growing a lot of cucurbits in one place makes you an obvious target. Presumably, these SVBs found me by smell, and my garden reeks of mature cucurbits. Had I realized the risk, I’d have cut back.
Prevention: Before the moth shows up.
It’s tough to separate truth from folklore here but let me try.
The usual advice for plant pests holds: Rotate crops, destroy infected plants, and so on. All of that matters strongly here, because the moth will pupate and overwinter in the soil otherwise. And then not only is your crop toast the next year, you’ve created a problem for everybody within a mile radius.
Also, well worth noting: Around here, in theory, you can just skip this whole hassle by planting your cucurbits late, on or about July 1. We have an adequately long growing season that you’ll still get yield. You lose bragging rights. You probably lose some yield.* But if you plant now-ish, the SVB will have come and gone by the time your plants are up and are targets. I’m still weighing that approach for next year.
* Just do the math. Sunlight is the energy input. If no other factors (e.g., frost, low temps, lack of rain, damnable insects) limit yield, then it’s all about having leaf area out there to collect sunlight. Longest day of the year is June 21 or so. Best of all possible worlds, every square foot of your garden is covered by leaves of food-producing plants, as of June 21. But let’s say you push that same leaf cover to, say late August, by planting a couple of months late. What’s the difference in energy input, over the (say) month-long productive life of your squash plant? Look up the insolation. Courtesy of this reference, from the National Renewable Energy Labs, we see that in Richmond VA July total sunlight rates about 20,000 on whatever-the-heck that scale is (kilojoules per square meter), but September rates just 15,000 on that same scale. From which you can plausibly infer that yields of late-planted summer squash will be maybe 75% of the yields of spring-planted summer squash. So in the end, all of this bullshit, dealing with the SVB, is about 25% of my yield of summer squash. And the timing thereof. Just to put it into perspective. If I lose more than 25% of my summer squash to the SVB, then its smarter to plant my summer squash mid-summer, rather than spring. Really, I could just plant more, later, right?
I have yet to find a source that will definitively say that this approach works here in Virginia. I.e., a source that says there’s only (say) a two-week window when the SVB moth is active. But if so, it seems to me that just avoiding this SVB fight beats the heck out of where I am now, which is trying to figure out a way to save my spring-planted squash and pumpkins. But I’m the sort of gardener that’ll just tear up and throw away plants that get infested with bugs.
Wrapping the stem of the plant in aluminum foil shows up a lot. Alternatively, wrapping it in panty hose. That is, protect the lower stem of the plant by wrapping it in tin foil. That way the SVB can’t deposit eggs on the plant and/or the larvae can’t get to the stem to enter it. I’ve seen other physical barriers mentioned, but (aside from Tanglefoot, discussed below) nothing that seems to beat this.
I’ve seen people put in a barrier that’s a couple of inches up. And buried a bit in the soil. I’ve seen people wrap the first foot of the stem.
Of those, based on my observation, I can verify that I’d use the wrap-the-first-foot-of-the-stem approach. And bury it in the soil a bit. That’s because this morning, I caught an SVB moth ovipositing on a pumpkin that was next to a sunflower, in my garden. The damned thing was actually hitting the sunflower stalk out of confusion, laying eggs easily 10″ up the stalk, well away from the ground. So while they may prefer to lay eggs at the base of a stalk, they will surely lay them quite a distance up the stalk. Covering the first 2″ with tin foil will help, but I think that the folks who cover the first foot of stalk have probably dealt with moths that were doing what my moths were doing, this AM: Depositing eggs well away from the ground surface.
Unfortunately, I don’t think that works well with summer squash. At least, not with what I’ve got growing. At this point, the main stems are maybe 2″ across, filled with leaf stalks leaving the stem, and sitting directly on the ground. Tin foil might have worked when they were tiny little plants, but now, huge portions of the main stem are exposed, and there’s no way to prevent that with tin foil. So I suspect that this method works with vining squash, but not with summer squash. My summer squash “stems” are like water distribution manifolds. There’s no way to cover them with tin foil.
Yellow traps. The idea here is to put out some type of yellow trap — bowl of soapy water, sticky trap, and so on — that the SVB moths will be attracted to. My only and major concern is that bees are attracted to yellow as well. Based on a couple of reports, I would not do this, as it is not sufficiently selective.
Tanglefoot on the plant stems. This is an another non-selective method, but without anything to attract bees. This seems like a better approach, to me. I would also consider leaving traps based on craft paper covered with Tanglefoot, or craft paper around the plant stem, covered with Tanglefoot. These would only catch insects attracted to the plant stems.
Diatomaceous earth. I have yet to figure out what this is supposed to do. I’m not sure whether this is a preventative targeting killing the SVB moth, or whether it’s there to kill the larvae when they hatch. Either way, this washes off and must be re-applied after every rain (and, I guess, after every watering).
Trap crops, resistant varieties, and repellent crops. I’ve seen trap crops mentioned, mostly for commercial farms. Blue Hubbard squash is the preferred variety, but some people suggest using zucchini as the trap crop. Some varieties are known to be unattractive to SVB (e.g., butternut squash). I have seen one reference suggesting that you interplant cucumbers with other cucurbits, as the SVB reportedly will avoid cucumbers as being a poor target.
Cure: After the moth shows up.
Killing the moths by hand is laudable. But ain’t no way you’re going to get them all. So this is all about dealing with the eggs hatching on your plants.
Of course, the trick here is to kill the resulting larvae, but not the beneficial insects in your garden. Of which, bees are clearly the #1 concern for me.
I’m ruling out Sevin and similar. If you’re into that, go for it. Put enough of that crap down, presumably you can kill everything in its path, and still have plants that survive it.
Pyrethrins similarly have a high bee toxicity.
Spinosad has been tested and found to be as effective as pyrethrins. Still, in a commercial setting, all this does is reduce the total amount of damage. It does not guarantee that all plants will survive. The great advantage here is that this is known to be effective.
Neem gets several mentions, but it’s not clear exactly how that works. The single best testimonial I saw suggests that using neem as a systemic insecticide is effective. To me, this suggests that neem may work, in part, by poisoning the larvae that manage to get past your other methods and burrow into the stem.
My approach this year.
It was too late for preventive measures. Or so I thought, based on the assumption that the SVB moth would only be around for a week or so. I am in the process of re-thinking that.
I started with piece-meal spraying of low-volume spinosad, at the bases of the stems. I stepped that up to spraying the entire set of cucurbits, and all of the stems at ground level up to a couple of feet, with a higher-concentration spinosad solution made up from concentrate, according to manufacturer’s directions.
The first ready-mixed spinosad solution was listed as 0.001% spinosad (Captain Jacks Deadbug Juice, of all things). The product I am now using is 8 times more concentrated, when mixed according to directions. what I am using now works out to be 0.008% spinosad (2 ounces of 0.5% spinosad solution per gallon of water). I am quite surprised that there is this much variation in the concentration of the active ingredient. But I am working strictly by the directions.
So far, effect on bees appears non-existent. Not only no dead bees, but tons of bumblebees and handfuls of honeybees.
Spinosad has limits. Mostly, it only lasts 5-7 days, and commercial growers can only use it for a few sprayings per year on any one crop. That said, presumably they spray the entire plant. I’m not sure this limitation applies to selectively spraying stems only. In addition, you must wait three days before harvesting squash, based on the package directions. Again, I assume that’s based on commercial sprayers spraying the entire plant. That said, I harvest everything of any size before I spray, and I wait the three days before harvesting again.
Based on a selective reading of the literature, I’m going to add neem oil to this. I could not find any estimate of effectiveness of neem in this use. I did find one fairly convincing testimonial. I plan to spray the lower stems, and mostly, I plan to soak some into the soil at the base of the stems, as the active ingredient in neem is readily absorbed by the root systems of most plants (but only weakly absorbed by the leaves). I hope to make the plant stems toxic to any borers that manage to get past the spinosad.
What I’m going to do next year.
If the SVB moth season is short, I’m just going to plant around it. If the SVB season is longer, I will implement some of the moth-trapping strategies, probably starting with craft paper covered with Tanglefoot around the bases of the squash plants. Or just skip planting squash and pumpkins for a year or two.